This generates the following on build:BUILD VERSION: v0.1-1-gc5c911c-dirty-timv@timv-5510-27/04/2019-23:30
which I can include as a string literal in my datalog files with PIO_BUILD

My problem is that this causes PIO to rebuild the entire project, not just compilation units that depend on PIO_BUILD (only one). This makes the build process quite slow, as there are a number of dependencies.